This disclosure relates to channel estimation in wireless communication systems, including Wireless Local Area Networks (WLANs).
Wireless communication systems can include multiple wireless communication devices that communicate over one or more wireless channels. When operating in an infrastructure mode, a wireless communication device called an access point (AP) provides connectivity with a network, such as the Internet, to other wireless communication devices, which can be referred to as client stations (STAs), client devices, clients, or access terminals (ATs). Various examples of wireless communication devices include mobile phones, smart phones, wireless routers, and wireless hubs. In some cases, wireless communication electronics are integrated with data processing equipment such as laptops, personal digital assistants, and computers.
Wireless communication devices in a WLAN can use one or more protocols for a medium access control (MAC) layer and a physical (PHY) layer. For example, a wireless communication device can use a Carrier Sense Multiple Access (CSMA) with Collision Avoidance (CA) based protocol for a MAC layer and Orthogonal Frequency Division Multiplexing (OFDM) for the PHY layer. The MAC layer can communicate with a Physical Layer Convergence Protocol (PLCP) sublayer. After receiving a MAC protocol data unit (MPDU) from the MAC layer, the PLCP sublayer can include PHY specific preamble fields to form a PLCP protocol data unit (PPDU) for transmission. A MPDU can also be called a PLCP service data unit (PSDU). A PPDU can include one or more training fields to enable channel estimation at a receiver.
Wireless communication systems, such as WLANs, can use one or more wireless communication technologies, such as OFDM for a PHY layer. In an OFDM based wireless communication system, a data stream can be split into multiple data substreams. Such data substreams are sent over different OFDM subcarriers, which are commonly also referred to as tones or frequency tones. WLANs such as those defined in the Institute of Electrical and Electronics Engineers (IEEE) wireless communications standards, e.g., IEEE 802.11n, and IEEE 802.11ac, can use OFDM to transmit and receive signals.